I'd suggest not to add too much new stuff to the pfd.nas file, its structure is going to cause challenges in the future if we continue building onto it as is - it would be better to either look at TorstenD's recent PFD work and reuse certain SVG/animation building blocks from there, or at least adopt the suggestions detailed at:
http://wiki.flightgear.org/Howto:Coding ... _FrameworkOverall, there's no reason why shouldn't be able to generalize navdisplay.mfd a little better and reuse the same method to also allow PFDs, and other MFDs, to be scripted like this - back-end wise, we could then adopt either Torsten's or Philosopher's Canvas/animation helpers. Creating single-instance MFDs with global state is not a good idea, and will lock out any other aircraft developers who could normally reuse the same code for their own aircraft/instruments.
I don't think there's too much missing to allow most MFDs to be developed primarrly in Inkscape, and scripted via Nasal extension hooks, analogous to those developed by Torsten for the ZivkoEdge - if we want to support styling and customization, we can still use the ND method until better methods become available.